In current imaging systems flickering lighting and objects with changing illumination in an image may result in missing parts of an object, or object distortion. In particular, light-emitting diode (LED) traffic signs (which can flicker several hundred times per second), and LED stop and head lights of modern cars, have been widely adopted for traffic control signs and vehicle components. However, these LEDs present detection issues for current image processing systems. Typically, image sensors acquire light asynchronously relative to the scenery being captured. This means that portions of an image may not be exposed for part of the frame duration. This is especially true for objects with illumination flickering when integration times are much shorter than the flicker periods. Zones in an image that are not fully exposed to dynamic scenery may result in object distortion, saturation data loss, and color artifacts.
Vehicle cameras are required to be able to capture images with a wide dynamic range (WDR) of light conditions, such as entering or exiting tunnels. Most of these cameras are equipped with a CMOS sensor with WDR technology. The concept of this WDR sensor is to capture an image by combining multiple exposure frames, with each exposure frame having different exposure duration. A WDR module composites images by selecting the short-exposure frames for the areas of movement, as well as oversaturated areas, within an input image, while the dark areas, as well as non-moving areas (without brightness oversaturation) are synthesized by the long-exposure frames.
Short exposure times will sometimes cause the image sensor to miss the LED “on” pulse and then cause the image to have flickering artifacts, as shown in the following figure. This flickering issue not only affects the viewing experience but also may degrade the accuracy of judgement in a system like Advanced Driver Assistance System (ADAS).